The use of orbital tools has become widespread. For example, detail sanders having orbital sanding heads are used for performing specific finishing tasks such as sanding edges adjacent internal walls. To perform such tasks, the tools utilized must have controlled finite movement in a confined area so as to fine sand the desired area without damaging the surface upon which the work is being performed. Various approaches have been taken to perform the difficult task of sanding these internal corners and other hard to reach areas which require fine sanding or abrasion. Further, there are other applications for orbital tools, such as rough wood working sanders and auto body sanders.
Orbital tools utilize center pivot mechanisms to orbit or vibrate the working member of the tool. Some of these orbital tools, such as detail sanders, employ constrained pivoting mechanisms which prevent the working member of the orbital tool from freely rotating relative to the housing. Others of these orbital tools, such as rough wood working and auto body sanders, employ random pivoting mechanisms which permit the working member to freely rotate relative to the housing.
One example of an orbital tool is described in U.S. Pat. No. 4,744,177 issued to Braun et al. The Braun et al. patent describes an orbital tool with a center pivot mechanism that changes the eccentricity of the working member axis, or the working offset, by reversing motor direction to rotate an intermediate member 180 degrees relative to the drive shaft about a drive shaft eccentric axis. The 180 degree rotation moves the working member axis to a different working offset on the other side of the drive shaft central axis.
A disadvantage associated with existing orbital tools is the fact that dust, dirt, and other debris often find their way into the center pivot mechanism, causing poor performance and premature wear. Another disadvantage is that existing pivot mechanisms do not allow a single orbital tool to have a variety of different working members, in addition to adjustable eccentricity. Yet another disadvantage associated with existing orbital tools, including those with adjustable eccentricity mechanisms, is that a high moment of inertia about the eccentric axis due to the intermediate and working members causes excessive component loading and wear, particularly during motor reversing.